Thin Film Layers Having Non-Uniform Thicknesses

This application is a divisional of U.S. patent application Ser. No. 18/532,594, filed Dec. 7, 2023, which claims the benefit of U.S. Provisional Application Ser. No. 63/386,704, filed Dec. 9, 2022, each of which is hereby incorporated by reference in its entirety.

The present disclosure relates to diffractive elements positioned over an area of a light-guiding surface of a light guide, and techniques for manufacturing such diffractive elements.

An augmented reality headset may include at least one display that can display additional content to the user, which can appear to the user as being superimposed on real-world objects proximate the user. There is ongoing effort to improve augmented reality headsets.

Corresponding reference characters indicate corresponding parts throughout the several views. Elements in the drawings are not necessarily drawn to scale. The configurations shown in the drawings are merely examples and should not be construed as limiting in any manner.

An augmented reality headset can include two displays. Each display can be located proximate a respective eye of a user. The displays can be worn, such as in the form of spectacles or a headset. Each display can be at least partially transparent, such that the user can observe real-world objects proximate the user through each display. Each display can display additional content to the user, which can appear to the user as being superimposed on the real-world objects proximate the user.

In an example of augmented reality display, a light source can direct light into a light guide. The light guide can extend over a surface area of the display. The light guide can guide light as guided light from the light source to all, most, or at least some of the surface area of the light guide. Diffractive elements, distributed over the surface area of the light guide, can extract at least some of the guided light from the light guide and direct the extracted light toward an eye of the user. The light extracted from the light guide by the diffractive elements provides additional content to the user. Because the diffractive elements may occupy a relatively small fraction of the surface area of the light guide, the remaining surface area of the light guide can be at least partially transparent, which can allow the user to view the surrounding real-world objects through the light guide.

To help avoid having differences in brightness over the surface area of the display, such as a portion of the display relatively close to the light source being brighter than another portion of the display that is relatively far from the light source, the diffractive elements can vary in size and/or shape over the surface area of the light guide. For example, a diffractive element that is relatively close to the light source may be shaped and sized to have a relatively low diffraction efficiency (e.g., a value between zero and one representing a fraction of incident light that is coupled into a specified diffractive order), while a diffractive element that is relatively far from the light source may be shaped and sized to have a relatively high diffraction efficiency.

1 3 FIGS.- 4 15 FIGS.- 16 23 FIGS.- show an example of an illumination system, including diffractive elements that can vary in at least one of size and shape.show an example of a manufacturing technique that can produce the illumination system, including the diffractive elements that can vary in at least one of size and shape.show another example of a manufacturing technique that can produce the illumination system, including the diffractive elements that can vary in at least one of size and shape. Both manufacturing techniques make use of thin-film stacks that include one or more layers having a non-uniform thickness.

For example, in a thin film stack deposited on a substrate, a first layer can have a non-uniform thickness. A second layer, disposed so that the first layer is between the substrate and the second layer, can have a non-uniform thickness. A first pattern can be formed on the second layer to define first areas. The second layer can be etched in the first areas to form first holes having varying depths. A second pattern can be formed on the first layer in the first holes to define second areas. Each second area can be smaller than a corresponding first area. The first layer can be etched in the second areas to form second holes having varying depths. An imprint of the etched thin film stack can be formed such that the first holes and the second holes form a plurality of diffractive elements having varying sizes on the imprint.

1 FIG. 100 100 shows a side view of an example of an illumination system. The illumination systemcan utilize diffractive elements having non-uniform properties, such as at least one of size and shape, over or within a specified surface area thereof. The non-uniform properties can at least partially compensate for non-uniformities in brightness that can arise as a function of distance away from a light source.

100 102 102 102 106 106 106 100 102 106 106 102 106 102 102 106 102 102 The illumination systemcan include a light guide. The light guidemay be referred to as a waveguide. For the purposes of this document, the terms light guide and waveguide are used interchangeably. The light guidecan be configured as a planar light guide, with light guiding surfaces, such as a light-guiding surfaceA and an opposing light-guiding surfaceB. During operation of the illumination system, the light guidecan guide guided light via total internal reflection from the light-guiding surfaceA and the light-guiding surfaceB. In some examples, the light guidecan be planar, such that the light guiding surfacesare planar and parallel. In other examples, the light guidecan be curved with a relatively large radius of curvature. For example, the light guidecan optionally be shaped in the form of a spectacle lens, which has opposing light guiding surfacesthat are both curved outward from a user's eye to avoid contact with the user's eyelashes. The light guidecan be formed from a material that is transparent or at least partially transparent for wavelengths in the visible portion of the electromagnetic spectrum, such as between about 400 nm and about 700 nm. Suitable materials for the light guideinclude glass, fused silica, an optical plastic such as polycarbonate, and others.

100 104 106 102 104 106 104 106 104 108 106 110 108 100 104 104 104 100 104 1 FIG. 1 FIG. The illumination systemcan include a plurality of diffractive elementspositioned over or within an area of a light-guiding surfaceof the light guide. In the configuration of, the diffractive elementsare positioned over an area of the light-guiding surfaceA. Alternatively, the diffractive elementscan be positioned over an area of the light-guiding surfaceB. Each diffractive elementincludes a lower elementextending from the light-guiding surfaceand an upper elementextending from the lower element.shows the illumination systemas including three diffractive elementsA,B, andC. In practice, an actual illumination systemcan include significantly more than three diffractive elements, such as hundreds or thousands of diffractive elements.

100 112 118 106 102 112 114 102 102 114 112 112 102 The illumination systemcan include a light sourcedisposed at a first edgeof the light-guiding surfacesof the light guide. Suitable light sources can include light emitting diodes, such as white light emitting diodes or single-wavelength light emitting diodes, such as red light emitting diodes, green light emitting diodes, and blue light emitting diodes, laser diodes, or other suitable light sources. The light sourcedirects lightinto the light guide. The light guideis configured to guide lightfrom the light source as guided light. The light sourcemay be referred to as a projector or light engine, which may include a reflective, transmissive, or emissive display panel, such as a liquid crystal on silicon (LCoS) or microLED display. The light sourcemay also include optics, such as one or more lenses, to focus an image from the display panel as a pupil onto an input grating of the light guide.

104 114 102 116 104 114 112 118 106 114 102 114 102 104 114 102 114 112 112 114 104 116 116 102 114 114 104 116 116 102 114 114 104 116 116 102 The diffractive elementsextract guided lightout of the light guideas extracted light. The diffractive elementscan vary in at least one of size and shape. As the lightpropagates away from the light source, such as with increasing distance along the Y-axis away from the first edgeof the light-guiding surfaces, the amount of lightwithin the light guidedecreases. The “amount” of guided lightcorresponds to the energy of the guided light in the light guide, with the amount of energy decreasing as diffractive elementsextract guided lightout of the light guideas the guided lightpropagates away from the light source. For example, near the light source, the first amount of lightA can be relatively high. A first diffractive elementA extracts some light, such as extracted portion of lightA, out of the light guide, such that a second amount of lightB is less than the first amount of lightA. A second diffractive elementB also extracts some light, such as extracted portion of lightB, out of the light guide, such that a third amount of lightC is less than the second amount of lightB. A third diffractive elementC also extracts some light, such as extracted portion of lightC, out of the light guide, and so forth.

104 102 116 104 116 104 114 116 104 106 102 104 114 116 106 102 It should be noted that in practice, the diffractive elementsmay not individually extract light from the light guideto produce the extracted light, but may act in concert with adjacent diffractive elementsto produce the extracted light. For example, the diffractive elementscan be spaced with a spacing that allows the lightto be directed into extracted lighthaving a specified propagation direction or a specified range of propagation directions. The diffractive elementscan have a size and shape that vary over a surface area of the light-guiding surfaceof the light guide. The size and shape of the diffractive elementscan determine, at least in part, how much of the lightis extracted to form the extracted light, as a function of location across the light-guiding surfaceof the light guide.

2 FIG. 3 FIG. 2 FIG. 104 104 108 110 104 106 102 shows a side-view drawing of an example of a diffractive element.shows a top-view drawing of the diffractive elementof. In some examples, the lower elementand the upper elementof each diffractive elementare substantially orthogonal to the light-guiding surfaceof the light guide.

108 106 102 108 208 106 102 110 106 102 110 210 106 102 The lower elementcan have a lower height (LH) in a direction orthogonal to the light-guiding surfaceof the light guide. The lower elementcan have a lower cross-sectional area (LA), such as on a surface, in a plane parallel to the light-guiding surfaceof the light guide. The upper elementcan have an upper height (UH) in the direction orthogonal to the light-guiding surfaceof the light guide. The upper elementcan have an upper cross-sectional area (UA), such as on a surface, in the plane parallel to the light-guiding surfaceof the light guide. The upper cross-sectional area (UA) can be less than the lower cross-sectional area (LA).

104 106 102 108 104 108 104 108 104 110 104 110 104 110 104 104 106 102 1 FIG. 1 FIG. 1 FIG. The lower heights (LH) and the upper heights (UH) of the plurality of diffractive elementscan vary over the area of the light-guiding surfaceof the light guide. For example, in the example of, the lower height (LH) of a first lower elementA of the first diffractive elementA is less than a lower height of a second lower elementB of the second diffractive elementB, which in turn can be less than a lower height of a third lower elementC of the third diffractive elementC. Likewise, in the example of, the upper height of a first upper elementA of the first diffractive elementA can be greater than an upper height of a second upper elementB of the second diffractive elementB, which in turn can be greater than an upper height of a third upper elementC of the third diffractive elementC. The configuration ofis but one example of how the sizes and shapes of the diffractive elementscan vary over a surface area of a light-guiding surfaceof the light guide. Other configurations can also be used.

104 116 In some examples, the diffractive elementscan have lower heights (LH), lower cross-sectional areas (LA), upper heights (UH), and upper cross-sectional areas (UA) selected such that the extracted light portions, such as light, have values of optical power per area that are substantially equal or tunable in a way that is beneficial for the optical design, such as by making a background appear more uniform or making an image appear more accurate.

104 118 106 102 118 106 102 118 106 102 In some examples, the lower heights (LH) of the diffractive elementscan vary monotonically as a function of distance away from the first edgeof the light-guiding surfaceof the light guide. For example, the lower heights (LH) can increase or remain constant as a function of distance away from the first edgeof the light-guiding surfaceof the light guide. As another example, the lower heights (LH) can decrease or remain constant as a function of distance away from the first edgeof the light-guiding surfaceof the light guide.

104 118 106 102 118 106 102 118 106 102 In some examples, the upper heights (UH) of the diffractive elementscan vary monotonically as a function of distance away from the first edgeof the light-guiding surfaceof the light guide. For example, the upper heights (UH) can increase or remain constant as a function of distance away from the first edgeof the light-guiding surfaceof the light guide. As another example, the upper heights (UH) can decrease or remain constant as a function of distance away from the first edgeof the light-guiding surfaceof the light guide.

4 15 FIGS.- 1 FIG. 4 15 FIGS.- 4 15 FIGS.- 1 FIG. 100 104 100 show an example of a manufacturing technique that can produce the illumination system, such as illumination systemof, including the diffractive elementsthat can vary in at least one of size and/or shape over a surface area of a light guide. The technique ofcan produce other illumination systems as well. The technique ofis but one manufacturing technique to produce the illumination systemof. Other manufacturing techniques can also be used.

4 FIG. 4 FIG. 400 402 402 402 shows a side-view cross-section of an illumination systemafter a first stage of assembly. In, a substrateis provided. In some examples, the substratecan include a layer of base material, such as silicon, quartz, glass, or another suitable material. In some examples, the base layer can have a thickness between about 0.1 mm and about 10 mm. In some examples, the base layer can be a wafer having a diameter of 100 mm, 150 mm, 200 mm, 300 mm, 400 mm, or another suitable value. During subsequent assembly stages, a thin film stack may be deposited on the substrate, as will be described in more detail below.

5 FIG. 5 FIG. 500 502 402 502 502 402 502 602 802 502 104 2 shows a side-view cross-section of an illumination systemafter a second stage of assembly. In, a first layerhas been deposited on the substrate. In some examples, the first layercan function as an etch stop layer. In some examples, the first layercan be formed from a material that is resistant to an etchant that may be used on subsequently deposited layers during the process of forming a desired pattern in or on the substrate. In some examples, the first layercan include an etch stop material, such as silicon dioxide (SiO). The etch stop material can be significantly less susceptible to etchant compared with etchable layers, such as layerand, as discussed in more detail below. In some examples, the first layercan resist being etched longer than the etchable layers by a factor of at least ten, at least twenty, at least thirty times, at least 40, at least 50, at least 100, or another suitable factor. Such resistance to etching can improve dimensional control of the diffractive elementsprepared using a thin film stack as disclosed herein according to embodiments of the present disclosure.

502 502 502 In some examples, the first layercan have a uniform thickness. In some examples, the first layercan be applied by sputter coating, vapor phase deposition, or another suitable coating process. In some examples, the first layercan have a thickness between about 5 nm and about 50 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, or another suitable thickness value.

6 FIG. 6 FIG. 600 602 502 602 602 602 602 602 shows a side-view cross-section of an illumination systemafter a third stage of assembly. In, a second layerhas been deposited on the first layer. In some examples, the second layercan be deposited via graded sputtering or another suitable technique, such that the second layercan have a non-uniform thickness. In some examples, the second layercan be an etchtable or etch layer. In some examples, the second layeris formed from a material that is susceptible to etchant (i.e., is etchable). In some examples, the second layercan be formed from amorphous silicon (Si), or another suitable material.

602 602 402 1 3 FIGS.- In some examples, the second layercan have a thickness that is greater than 25 nm, greater than 30 nm, greater than 35 nm, greater than 40 nm, greater than 45 nm, greater than 50 nm, greater than 55 nm, greater than 60 nm, greater than 65 nm, greater than 70 nm, greater than 75 nm, or has another suitable value of thickness. In some examples, the second layercan have a thickness that varies between about 10 nm and about 1000 nm across a width of the substrate(in the X-Y plane of).

602 402 402 602 602 402 402 602 402 402 402 602 402 602 402 In some examples, the second layercan have a thickness profile having a linear gradient in a ratio of about 10:1 across a width of thestrate. In some examples, the second layercan have a first region over which the layer thickness is a constant first value and a second region over which the layer thickness varies from the first value to a second value. In some examples, the second layercan have a thickness profile having a constant thickness of about 65 nm for about 20% of a width of the substrate, with a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the second layercan have a thickness profile having a constant thickness of about 50 nm for about 15% of a width of the substrate, a constant thickness of about 65 nm thickness for about 5% of the width of the substrate, a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the second layercan have a thickness profile having an inverse square decay from about 65 nm to about 25 nm across a width of the substrate. In some examples, the second layercan have a thickness profile having an exponential decay from about 65 nm to about 25 nm across a width of the substrate. Other thickness profiles can also be used.

7 FIG. 7 FIG. 700 702 602 702 702 402 702 702 702 702 2 shows a side-view cross-section of an illumination systemafter a fourth stage of assembly. In, a third layerhas been deposited on the second layer. In some examples, the third layercan function as an etch stop layer. In some examples, the third layercan be formed from a material that is resistant to an etchant that may be used on subsequently deposited layers during the process of forming a desired pattern in or on the substrate. In some examples, the third layercan include an etch stop material, such as silicon dioxide (SiO). In some examples, the third layercan have a uniform thickness. In some examples, the third layercan be applied by sputter coating, vapor phase deposition, or another suitable coating process. In some examples, the third layercan have a thickness between about 5 nm and about 50 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, or another suitable thickness value.

8 FIG. 8 FIG. 800 802 702 802 802 802 802 802 shows a side-view cross-section of an illumination systemafter a fifth stage of assembly. In, a fourth layerhas been deposited on the third layer. In some examples, the fourth layercan be deposited via graded sputtering or another suitable technique, such that the fourth layercan have a non-uniform thickness. In some examples, the fourth layercan be an etch layer. In some examples, the fourth layercan be formed from a material that is susceptible to etchant (e.g., is etchable). In some examples, the fourth layercan be formed from amorphous silicon (Si), or another suitable material.

802 802 402 In some examples, the fourth layercan have a thickness that is greater than 25 nm, greater than 30 nm, greater than 35 nm, greater than 40 nm, greater than 45 nm, greater than 50 nm, greater than 55 nm, greater than 60 nm, greater than 65 nm, greater than 70 nm, greater than 75 nm, or has another suitable value of thickness. In some examples, the fourth layercan have a thickness that varies between about 10 nm and about 1000 nm across a width of the substrate.

802 402 402 802 802 402 402 802 402 402 402 802 402 802 402 802 602 In some examples, the fourth layercan have a thickness profile having a linear gradient in a ratio of about 10:1 across a width of thestrate. In some examples, the fourth layercan have a first region over which the layer thickness is a constant first value and a second region over which the layer thickness varies from the first value to a second value. In some examples, the fourth layercan have a thickness profile having a constant thickness of about 65 nm for about 20% of a width of the substrate, with a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the fourth layercan have a thickness profile having a constant thickness of about 50 nm for about 15% of a width of the substrate, a constant thickness of about 65 nm thickness for about 5% of the width of the substrate, a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the fourth layercan have a thickness profile having an inverse square decay from about 65 nm to about 25 nm across a width of the substrate. In some examples, the fourth layercan have a thickness profile having an exponential decay from about 65 nm to about 25 nm across a width of the substrate. Other thickness profiles can also be used. In some examples, the thickness profile of the fourth layercan differ from the thickness profile of the second layer.

9 FIG. 2 3 FIGS.and 2 3 FIGS.and 900 802 208 210 106 110 108 110 108 shows a side-view cross-section of an illumination systemafter a sixth stage of assembly. A first mask layer (not shown) has been applied over the fourth layer. Electron-beam lithography (or another suitable technique) has defined a first pattern in the first mask layer to define first areas. In some examples, the first areas correspond to areas of the first mask layers that have been removed. In other examples, the first areas correspond to areas of the first mask layer that remain after other areas of the first mask layer have been removed. The first areas can correspond to a combination of the lower cross-sectional area (LA), such as on the surface() and the upper cross-sectional area (UA), such as on the surface(). In other words, the first areas can correspond to areas in the plane of the light-guiding surfacethat include cross-sectional areas (LA), (UA) of both the upper elementsand the lower elements. Subsequent stages will define second areas within the first areas, to distinguish the upper elementsfrom the lower elements.

802 802 702 702 6 After the first areas have been defined, the fourth layercan be exposed to a dry etching process, such as reactive ion etching (RIE), inductively coupled plasma etching (ICP), atomic layer etching (ALE), or deep reactive ion etching (DRIE). The etching can use an etchant such as a bromine-based plasma, a chlorine-based plasma, a fluorine-based plasma, such as sulfur hexafluoride (SF), or another suitable material. The plasma can etch the fourth layerfully to the third layer. The third layercan be resistant to etching by the etchant and can therefore function as an etch stop layer.

802 802 902 6 After the fourth layerhas been etched, such as through deep reactive ion etching, using sulfur hexafluoride (SF) as an etchant, the fourth layerhas first holesin regions that correspond to the first areas.

10 FIG. 10 FIG. 1000 702 902 1002 702 1002 802 702 1002 3 shows a side-view cross-section of an illumination systemafter a seventh stage of assembly. In, the third layerhas been etched, such as with deep reactive ion etching, such as by using trifluoromethane (CHF). The etching has deepened the first holesto form deepened first holes. The etching can etch the holes fully through the third layer. The deepened first holescan have depths that correspond to the non-uniform thickness of the fourth layerplus the uniform thickness of the third layer. The deepened first holesmay also be referred to as simply first holes in the present description.

11 FIG. 1100 602 802 1002 shows a side-view cross-section of an illumination systemafter an eighth stage of assembly. A second mask layer (not shown) has been applied over the second layer(and remaining fourth layeras appropriate). Electron-beam lithography (or another suitable technique) has defined a second pattern in the second mask layer to define second areas within respective deepened first holes. Each second area can be smaller than a corresponding first area.

210 104 2 3 FIGS.and In some examples, the second areas correspond to areas of the second mask layers that have been removed. In other examples, the second areas correspond to areas of the second mask layer that remain after other areas of the second mask layer have been removed. The second areas correspond to the upper cross-sectional area (UA) on the surface() of the diffractive elements.

602 602 502 502 6 After the second areas have been defined, the second layercan be exposed to a dry etching process, such as reactive ion etching (RIE), inductively coupled plasma etching (ICP), atomic layer etching (ALE), or deep reactive ion etching (DRIE). The etching can use an etchant such as a bromine-based plasma, a chlorine-based plasma, a fluorine-based plasma, such as sulfur hexafluoride (SF), or another suitable material. The plasma can etch the second layerfully to the first layer. The first layercan be resistant to etching by the etchant, and therefore functions as an etch stop layer.

602 602 1102 6 After the second layerhas been etched, such as with deep reactive ion etching, such as by using sulfur hexafluoride (SF) as an etchant, the second layerhas second holesin regions that correspond to the second areas.

12 FIG. 12 FIG. 12 FIG. 8 FIG. 1200 502 1102 1202 502 1202 602 502 1202 402 502 802 3 shows a side-view cross-section of an illumination systemafter a ninth stage of assembly. In, the first layerhas been etched, such as with deep reactive ion etching, such as by using trifluoromethane (CHF). The etching deepens the second holesto form deepened second holes. The etching can etch the holes fully through the first layer. The deepened second holescan have depths that correspond to the non-uniform thickness of the second layerplus the uniform thickness of the first layer. The deepened second holesmay be referred to as simply second holes in the present description.illustrates an etched thin film stack, where the thin film stack is shown inand corresponds to the substrateand layers-formed on the substrate.

13 FIG. 1300 1302 802 1302 1002 1202 shows a side-view cross-section of an illumination systemafter a tenth stage of assembly. A material layerhas been deposited over the fourth layerand has filled in the volumes of the first and second holes defined by the earlier etching, to form an imprint of the etched thin film stack. In the imprint, the material of the material layerin the deepened first holesand the deepened second holeswill form a plurality of diffractive elements.

14 FIG. 14 FIG. 4 13 FIGS.- 1400 1302 402 502 602 702 802 1402 1402 shows a side-view cross-section of an illumination systemafter an eleventh stage of assembly. The material layerhas been separated from the thin film stack, which includes the substrate, the first layer, the second layer, the third layer, and the fourth layer, to form the imprint. The imprinthas been inverted top-to-bottom in, compared to the orientations shown in.

14 FIG. 15 FIG. 14 FIG. 14 FIG. 1402 102 1402 102 −7 Althoughshows the horizontal surfaces of the imprintas being angled away from being truly horizontal (and therefore angled away from being parallel to a surface of the light guidewhen the imprintis attached to the light guide, as shown below in), it should be noted that in practice, the angling may be extremely small. For example, for a layer that has a variation in thickness of 40 nm across a wafer having a diameter of 100 mm, the angling is 4×10radians, which is imperceptibly small. It will be understood that the angling away from horizontal inis retained merely for clarity and consistency with earlier drawings and does not imply that the surfaces inthat are shown as being angled away from horizontal are angled in any perceptible manner in practice.

15 FIG. 1 FIG. 9 10 FIGS.and 11 12 FIGS.and 1500 1402 102 1302 108 104 1402 1302 110 104 1402 shows a side-view cross-section of an illumination systemafter a twelfth stage of assembly. The imprinthas been attached to a light guideof. The portions of the material layerthat filled the first holes () form the lower elementsof the diffractive elementsdefined by the imprint. The portions of the material layerthe filled the second holes () form the upper elementsof the diffractive elementsdefined by the imprint.

104 104 108 110 104 108 110 108 108 110 110 15 FIG. As explained above, the variations in layer thicknesses and hole sizes create the desired variations in at least one of size and/or shape in the diffractive elements. For example, a first diffractive elementA includes first lower elementA and first upper elementA, while second diffractive elementB includes second lower elementB and second upper elementB. The first lower elementA and the second lower elementB can have a different size and/or a different shape and the first upper elementA and the second upper elementB can have a different size and/or a different shape, as seen in the example of.

9 12 FIGS.- 6 3 In some examples, the hole dimensions shown in, which are achieved using the etchable substrate with non-uniform etchable layer thicknesses interleaved with etch stop layers, can utilize a unique composition of the substrate. In other words, using defined mask layers to expose an underlying etchable substrate or an etch stop layer, respectively, rendering each successive layer susceptible to either SFor CHFetching, may achieve aspect ratio apertures that might not be possible by other processes, such as etching a monolithic substrate, for example.

4 15 FIGS.- Although two etchable layers and two accompanying etch stop layers are shown in, it will be understood that any suitable number of etchable layers and accompanying etch stop layers can also be used. Furthermore, the thickness profiles of respective layers may be modified according to the intended purpose.

104 104 104 104 4 15 FIGS.- Forming the diffractive elementsin the manner shown incan utilize wafer-level processes, which can reduce a cost of manufacturing devices that include the diffractive elements. Further, forming the diffractive elementsto have a variable size and/or variable shape can allow the diffractive elementsto extract light from the light guide to at least partially compensate for a reduction in optical power at increasing distances away from the light source, such as to present a more uniform brightness level to a user over the eyebox, which is the area (or volume) over which a user can perceive a projected image superimposed on the real-world view when moving their eye up, down, left and right.

4 15 FIGS.- 16 23 FIGS.- It is worthwhile to clarify the use of the term etch stop layer. Whereas the configuration ofincludes explicit etch stop layers (e.g., a layer having a sole function as a stopping layer that is not etchable for a particular etch process step), there are also configurations possible that lack explicit etch stop layers and instead use layer materials and etchants selected such that one or more layers can additionally function as an etch stop layer. For example, a first layer material may be etchable by a first etchant but not a second etchant, and a second layer material may be etchable by the second etchant but not the first etchant. By forming a layered stack with alternating layers of the first layer material and the second layer material, layers formed with the first layer material can function as etch stops (using the second etchant) for the layers formed with the second layer material, and layers formed with the second layer material can function as etch stops (using the first etchant) for the layers formed with the first layer material. Further, a substrate formed from a substrate material can function as one of the layers in the layered stack, with regard to etching and functioning as an etch stop for another layer. A detailed example is provided below, with regard to.

16 23 FIGS.- 1 FIG. 16 23 FIGS.- 16 23 FIGS.- 1 FIG. 100 104 100 show another example of a manufacturing technique that can produce the illumination system, such as illumination systemof, including the diffractive elementsthat can vary in at least one of size and shape over a surface area of a light guide. The technique ofcan produce other illumination systems as well. The technique ofis but one manufacturing technique to produce the illumination systemof. Other manufacturing techniques can also be used.

16 FIG. 16 FIG. 1600 1602 1602 1602 shows a side-view cross-section of an illumination systemafter a first stage of assembly. In, a substrateis provided. In some examples, the substratecan include a layer of base material, such as silicon, quartz, glass, or another suitable material. In some examples, the base layer can have a thickness between about 0.1 mm and about 10 mm. In some examples, the base layer can be a wafer having a diameter of 100 mm, 150 mm, 200 mm, 300 mm, 400 mm, or another suitable value. During subsequent assembly stages, a thin film stack may be deposited on the substrate, as will be described in more detail below.

17 FIG. 17 FIG. 1700 1702 1602 1702 1702 1702 1702 1702 2 shows a side-view cross-section of an illumination systemafter a second stage of assembly. In, a first layerhas been deposited on the substrate. In some examples, the first layercan be deposited via graded sputtering or another suitable technique, such that the first layercan have a non-uniform thickness. In some examples, the first layercan be an etch layer. In some examples, the first layeris formed from a material that is susceptible to etchant. In some examples, the first layercan be formed from amorphous silicon (Si), silicon dioxide (SiO), or another suitable material.

1702 1702 1602 1 3 FIGS.- In some examples, the first layercan have a thickness that is greater than 25 nm, greater than 30 nm, greater than 35 nm, greater than 40 nm, greater than 45 nm, greater than 50 nm, greater than 55 nm, greater than 60 nm, greater than 65 nm, greater than 70 nm, greater than 75 nm, or has another suitable value of thickness. In some examples, the first layercan have a thickness that varies between about 10 nm and about 1000 nm across a width of the substrate(in the X-Y plane of).

1702 1602 1702 1702 1602 1602 1702 1602 1602 1602 1702 1602 1702 1602 In some examples, the first layercan have a thickness profile having a linear gradient in a ratio of about 10:1 across a width of the substrate. In some examples, the first layercan have a first region over which the layer thickness is a constant first value and a second region over which the layer thickness varies from the first value to a second value. In some examples, the first layercan have a thickness profile having a constant thickness of about 65 nm for about 20% of a width of the substrate, with a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the first layercan have a thickness profile having a constant thickness of about 50 nm for about 15% of a width of the substrate, a constant thickness of about 65 nm thickness for about 5% of the width of the substrate, a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the first layercan have a thickness profile having an inverse square decay from about 65 nm to about 25 nm across a width of the substrate. In some examples, the first layercan have a thickness profile having an exponential decay from about 65 nm to about 25 nm across a width of the substrate. Other thickness profiles can also be used.

18 FIG. 18 FIG. 1800 1802 1702 1802 1802 1802 1802 1802 1702 1802 1702 1802 2 2 2 shows a side-view cross-section of an illumination systemafter a third stage of assembly. In, a second layerhas been deposited on the first layer. In some examples, the second layercan be deposited via graded sputtering or another suitable technique, such that the second layercan have a non-uniform thickness. In some examples, the second layercan be an etch layer. In some examples, the second layercan be formed from a material that is susceptible to etchant (e.g., is etchable). In some examples, the second layercan be formed from amorphous silicon (Si), silicon dioxide (SiO), or another suitable material. In some examples, the first layercan be formed from one of amorphous silicon (Si) or silicon dioxide (SiO), and the second layercan be formed from the other of amorphous silicon (Si) or silicon dioxide (SiO). In this manner the first layercan function as an etch stop layer for the second layer.

1802 1802 1602 In some examples, the second layercan have a thickness that is greater than 25 nm, greater than 30 nm, greater than 35 nm, greater than 40 nm, greater than 45 nm, greater than 50 nm, greater than 55 nm, greater than 60 nm, greater than 65 nm, greater than 70 nm, greater than 75 nm, or has another suitable value of thickness. In some examples, the second layercan have a thickness that varies between about 10 nm and about 1000 nm across a width of the substrate.

1802 1602 1802 1802 1602 1602 1802 1602 1602 1602 1802 1602 1802 1602 In some examples, the second layercan have a thickness profile having a linear gradient in a ratio of about 10:1 across a width of the substrate. In some examples, the second layercan have a first region over which the layer thickness is a constant first value and a second region over which the layer thickness varies from the first value to a second value. In some examples, the second layercan have a thickness profile having a constant thickness of about 65 nm for about 20% of a width of the substrate, with a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the second layercan have a thickness profile having a constant thickness of about 50 nm for about 15% of a width of the substrate, a constant thickness of about 65 nm thickness for about 5% of the width of the substrate, a linear taper from about 65 nm to about 25 nm for about 80% of the width of the substrate. In some examples, the second layercan have a thickness profile having an inverse square decay from about 65 nm to about 25 nm across a width of the substrate. In some examples, the second layercan have a thickness profile having an exponential decay from about 65 nm to about 25 nm across a width of the substrate. Other thickness profiles can also be used.

19 FIG. 2 3 FIGS.and 2 3 FIGS.and 1900 1802 208 210 110 108 110 108 shows a side-view cross-section of an illumination systemafter a fourth stage of assembly. A first mask layer (not shown) has been applied over the second layer. Electron-beam lithography (or another suitable technique) has defined a first pattern in the first mask layer to define first areas. In some examples, the first areas correspond to areas of the first mask layers that have been removed. In other examples, the first areas correspond to areas of the first mask layer that remain after other areas of the first mask layer have been removed. The first areas can correspond to a combination of the lower cross-sectional area (LA), such as on the surface() and the upper cross-sectional area (UA), such as on the surface(). In other words, the first areas can correspond to areas that include both the upper elementsand the lower elements. Subsequent stages will define second areas within the first areas, to distinguish the upper elementsfrom the lower elements.

1802 1802 1702 1702 1702 2 3 2 6 After the first areas have been defined, the second layercan be exposed to a dry etching process, such as reactive ion etching (RIE), inductively coupled plasma etching (ICP), atomic layer etching (ALE), or deep reactive ion etching (DRIE). The etching can use an etchant that can etch the material of the second layerbut not the material of the first layer. For example, if the first layeris amorphous silicon (Si) and the second layer is silicon dioxide (SiO), the etchant can be trifluoromethane (CHF), which etches silicon dioxide but not amorphous silicon. As another example, if the first layeris silicon dioxide (SiO) and the second layer is amorphous silicon (Si), the etchant can be sulfur hexafluoride (SF), which etches amorphous silicon but not silicon dioxide. Other etchants and material can also be used.

1802 1802 1902 After the second layerhas been etched, such as through deep reactive ion etching, the second layercan have first holesin regions that correspond to the first areas.

20 FIG. 2000 1702 1902 shows a side-view cross-section of an illumination systemafter a fifth stage of assembly. A second mask layer (not shown) has been applied over the first layer. Electron-beam lithography (or another suitable technique) has defined a second pattern in the second mask layer to define second areas within respective first holes. Each second area can be smaller than a corresponding first area.

210 2 3 FIGS.and In some examples, the second areas correspond to areas of the second mask layers that have been removed. In other examples, the second areas correspond to areas of the second mask layer that remain after other areas of the second mask layer have been removed. The second areas can correspond to the upper cross-sectional area (UA), such as on the surface().

1702 1702 1602 1602 After the second areas have been defined, the first layercan be exposed to a dry etching process, such as reactive ion etching (RIE), inductively coupled plasma etching (ICP), atomic layer etching (ALE), or deep reactive ion etching (DRIE). The etching can use an etchant as discussed above. The etchant can etch the first layerfully to the substrate. The substratecan be resistant to etching by the etchant and can therefore function as an etch stop layer.

1702 1702 2002 After the first layerhas been etched, such as with deep reactive ion etching, the first layercan have second holesthat correspond to the second areas.

21 FIG. 2100 2102 1802 2102 1902 2002 shows a side-view cross-section of an illumination systemafter a sixth stage of assembly. A material layerhas been deposited over the second layerand has filled in the volumes defined by the earlier etching, to form an imprint of the etched thin film stack. In the imprint, material of the material layerthat fills the first holesand the second holeswill form a plurality of diffractive elements on the imprint.

22 FIG. 21 FIG. 16 21 FIGS.- 2200 2102 1602 1702 1802 2202 2202 shows a side-view cross-section of an illumination systemafter a seventh stage of assembly. The material layerhas been separated from the thin film stack, which includes the substrate, the first layer, and the second layer, to form the imprint. The imprinthas been inverted top-to-bottom in, compared to the orientations shown in.

23 FIG. 2300 2202 102 2102 1902 108 104 2202 2102 2002 110 104 2202 shows a side-view cross-section of an illumination systemafter an eighth stage of assembly. The imprinthas been attached to a light guide. The material of the material layerthat fills first holes first holescan form the lower elementsof the diffractive elementsdefined by the imprint. The material of the material layerthat fills second holes second holescan form the upper elementsof the diffractive elementsdefined by the imprint.

104 104 108 110 104 108 110 108 108 110 110 As explained above, the variations in layer thicknesses and hole sizes can create the desired variations in at least one of size and shape in the diffractive elements. For example, a first diffractive elementA can include a first lower elementA and a first upper elementA. A second diffractive elementB can include a second lower elementB and a second upper elementB. The first lower elementA and the second lower elementB can have a different size and/or a different shape. The first upper elementA and the second upper elementB can have a different size and/or a different shape.

19 20 FIGS.- 6 3 In some examples, the hole dimensions shown in, which are achieved using the etchable substrate with non-uniform etchable layer thicknesses interleaved with etch stop layers, can utilize a unique composition of the substrate. In other words, using defined mask layers to expose an underlying etchable substrate or an etch stop layer, respectively, rendering each successive layer susceptible to either SFor CHFetching, may achieve aspect ratio apertures that might not be possible by other processes, such as etching a monolithic substrate, for example.

16 23 FIGS.- Although two etchable layers are shown in, it will be understood that any suitable number of etchable layers can also be used. Furthermore, the thickness profiles of respective layers may be modified according to the intended purpose.

104 104 104 104 16 23 FIGS.- Forming the diffractive elementsin the manner shown incan utilize wafer-level processes, which can reduce a cost of manufacturing devices that include the diffractive elements. Further, forming the diffractive elementsto have a variable size and/or variable shape can allow the diffractive elementsto extract light from the light guide to at least partially compensate for a reduction in optical power at increasing distances away from the light source, such as to present a more uniform brightness level to a user.

2000 1702 1802 20 FIG. In some examples, the illumination systemas depicted inmay be used without further processing. The materials used to define layersandmay have sufficiently similar refractive indices that light propagating along the length of the light guide by internal reflection may be selectively diffracted out of the light guide with increasing efficiency as the distance from the point of light entry increases.

24 FIG. 1 FIG. 2400 100 2400 shows a flow chart for an example of a methodfor generating a diffractive optical element, such as the illumination systemofor other suitable diffractive optical elements. The methodis but one example of a method for generating a diffractive optical element. Other suitable methods can also be used.

2402 2400 402 1602 602 1702 802 1802 At operation, the methodcan deposit a thin film stack on a substrate, such as substrateor substrate. The thin film stack can include a first layer, such as layeror layer, and a second layer, such as layeror layer. The first layer can be disposed between the substrate and the second layer. The first layer can have a non-uniform thickness. The second layer can have a non-uniform thickness.

2404 2400 At operation, the methodcan form a first pattern on the second layer to define first areas.

2406 2400 At operation, the methodcan etch the second layer in the first areas to form first holes.

2408 2400 At operation, the methodcan form a second pattern on the first layer in the first holes. The second pattern can define second areas.

2410 2400 At operation, the methodcan etch the first layer in the second areas to form second holes. The second holes can extend fully through the first layer to depths that correspond to the non-uniform thickness of the first layer.

2412 2400 At operation, the methodcan form an imprint of the etched thin film stack such that the first holes and the second holes form a plurality of diffractive elements on the imprint.

16 23 FIGS.- 16 23 FIGS.- 16 23 FIGS.- 16 23 FIGS.- 16 23 FIGS.- In some examples, such as the configuration of, the first layer can be formed from a first material and is deposited by graded sputtering. In some examples, such as the configuration of, the second layer can be formed from a second material different from the first material and is deposited by graded sputtering. In some examples, such as the configuration of, the second layer can be etched with deep reactive ion etching with a first etching material that etches the second material but not the first material. In some examples, such as the configuration of, the first layer can be etched with deep reactive ion etching with a second etching material that etches the first material but not the second material. In some examples, such as the configuration of, the first pattern and the second pattern are formed with electron-beam lithography.

16 23 FIGS.- In some examples, such as the configuration of, the second layer is deposited directly on the first layer with no intervening layers between the first layer and the second layer.

16 23 FIGS.- 16 23 FIGS.- In some examples, such as the configuration of, the first layer is deposited directly on a substrate with no intervening layers between the substrate and the first layer. In some examples, such as the configuration of, the second etching material may not etch a material of the substrate.

16 23 FIGS.- 2 3 6 In some examples, such as the configuration of, the first material is amorphous silicon (Si), the second material is silicon dioxide (SiO), the first etching material is trifluoromethane (CHF), and the second etching material is sulfur hexafluoride (SF).

16 23 FIGS.- 2 6 3 In some examples, such as the configuration of, the first material is silicon dioxide (SiO), the second material is amorphous silicon (Si), the first etching material is sulfur hexafluoride (SF), and the second etching material is trifluoromethane (CHF).

4 15 FIGS.- 2400 In some examples, such as the configuration of, the first layer can be formed from a first material and can be deposited by graded sputtering. The second layer can be formed from the first material and can be deposited by graded sputtering. A third layer can be disposed in the thin film stack between the first layer and the second layer. The third layer can be formed from a second material different from the first material. The first layer and the second layer can be etched with deep reactive ion etching with a first etching material that etches the first material but not the second material. The methodcan optionally further include etching the third layer in the first areas with deep reactive ion etching with a second etching material that etches the second material but not the first material, to deepen the first holes to depths that correspond to the non-uniform thickness of the second layer plus a thickness of the third layer.

4 15 FIGS.- 2400 In some examples, such as the configuration of, a fourth layer can be disposed in the thin film stack between the substrate and the first layer. The fourth layer can be formed from the second material. The methodcan optionally further include etching the fourth layer in the second areas with deep reactive ion etching with the second etching material, to deepen the second holes to depths that correspond to the non-uniform thickness of the first layer plus a thickness of the fourth layer.

4 15 FIGS.- In some examples, such as the configuration of, the third layer has a uniform thickness, the fourth layer has a uniform thickness, and the third layer and the fourth layer are deposited by sputtering.

4 15 FIGS.- In some examples, such as the configuration of, the fourth layer can be deposited on a substrate with no intervening layers between the substrate and the fourth layer. The second etching material may not etch a material of the substrate.

4 15 FIGS.- 2 3 6 In some examples, such as the configuration of, the first material can be amorphous silicon (Si), the second material can be silicon dioxide (SiO), the first etching material can be trifluoromethane (CHF), and the second etching material is sulfur hexafluoride (SF).

25 FIG. 1 FIG. 2500 100 2500 shows a flow chart for an example of a methodfor generating a diffractive optical element, such as the illumination systemofor other suitable diffractive optical elements. The methodis but one example of a method for generating a diffractive optical element. Other suitable methods can also be used.

2502 2500 2 At operation, the methodcan deposit, via sputtering, a first layer of silicon dioxide (SiO) on a substrate. The first layer can have a uniform thickness.

2504 2500 At operation, the methodcan deposit, via graded sputtering, a second layer of amorphous silicon (Si) on the first layer. The second layer can have a non-uniform thickness.

2506 2500 At operation, the methodcan deposit, via sputtering, a third layer of silicon dioxide on the second layer. The third layer can have a uniform thickness.

2508 2500 At operation, the methodcan deposit, via graded sputtering, a fourth layer of amorphous silicon on the third layer. The fourth layer can have a non-uniform thickness.

2510 2500 At operation, the methodcan form, with electron-beam lithography, a first pattern on the fourth layer to define first areas.

2512 2500 6 At operation, the methodcan etch, with deep reactive ion etching using sulfur hexafluoride (SF), the fourth layer in the first areas to form first holes.

2514 2500 3 At operation, the methodcan etch, with deep reactive ion etching using trifluoromethane (CHF), the third layer in the first areas to deepen the first holes to form deepened first holes. The deepened first holes can have depths that correspond to the non-uniform thickness of the fourth layer plus the uniform thickness of the third layer.

2516 2500 At operation, the methodcan form, with electron-beam lithography, a second pattern on the second layer within the deepened first holes to define second areas within respective deepened first holes.

2518 2500 At operation, the methodcan etch, with deep reactive ion etching using sulfur hexafluoride, the second layer in the second areas to form second holes.

2520 2500 At operation, the methodcan etch, with deep reactive ion etching using trifluoromethane, the first layer in the second areas to deepen the second holes to form deepened second holes. The deepened second holes can have depths that correspond to the non-uniform thickness of the second layer plus the uniform thickness of the first layer.

2522 2500 At optional operation, the methodcan form an imprint of the fourth layer, the third layer, the second layer, and the first layer such that the first deepened holes and the second deepened holes form a plurality of diffractive elements on the imprint. Each diffractive element can include a lower element extending from a base of the imprint and an upper element extending from the lower element. The lower elements can have lower heights that correspond to the non-uniform thickness of the fourth layer plus the uniform thickness of the third layer. The lower elements can have lower cross-sectional areas that correspond to the first areas. The upper elements can have upper heights that correspond to the non-uniform thickness of the second layer plus the uniform thickness of the first layer. The upper elements can have upper cross-sectional areas that correspond to the second areas.

4 15 FIGS.- In some examples, such as the configuration of, the second layer can have a thickness that varies monotonically from a first edge of the imprint to a second edge of the imprint. The fourth layer can have a thickness that varies monotonically from the first edge of the imprint to the second edge of the imprint.

1 25 FIGS.- 1 25 FIGS.- The structures and methods as described with reference tomay be used to prepare wafers, as will be understood by one skilled in the art of nanofabrication technology, to enable the preparation of multiple diffractive waveguide combiners (DWC) in a single operation. Each wafer can have a sufficient area to accommodate multiple DWCs. Each region of the wafer may be configured with specifically profiled etchable layers, as described with reference to, which are specific to a particular DWC nanostructure arrangement.

In some examples, each wafer may be used to produce a number of identical DWCs, with the wafer being configured with identical regions with respect to the variation in thickness profile across the region of each DWC.

In other examples, each wafer may be configured to prepare DWCs that are specific to a specific wavelength of light, for example, red, green, and blue, or red, green, cyan, and violet. In these examples, a single wafer may yield sufficient number of DWC elements necessary to produce a final waveguide design that includes stacked red, green, and blue, or stacked red, green, cyan, and violet-specific DWCs which can achieve a full color image when light is introduced.

The wafers produced according to the methods discussed above may subsequently be used in a step and repeat nano imprint lithography process to produce large quantities of DWC devices.

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments that can be practiced. These embodiments may also be referred to herein as “examples. ” Such embodiments or examples can include elements in addition to those shown or described. However, the present inventors also contemplate examples in which only those elements shown or described are provided. Moreover, the present inventors also contemplate examples using any combination or permutation of those elements shown or described (or one or more aspects thereof), either with respect to a particular example (or one or more aspects thereof), or with respect to other examples (or one or more aspects thereof) shown or described herein. That is, the above-described embodiments or examples or one or more aspects, features, or elements thereof can be used in combination with each other.

To further illustrate the systems and related methods disclosed herein, a non-limiting list of examples is provided below. Each of the following non-limiting examples can stand on its own or can be combined in any permutation or combination with any one or more of the other examples.

In Example 1, an illumination system can comprise: a light guide; and a plurality of diffractive elements positioned over an area of a light-guiding surface of the light guide, each diffractive element including a lower element extending from the light-guiding surface and an upper element extending from the lower element, the lower element having a lower height in a direction orthogonal to the light-guiding surface of the light guide, the lower element having a lower cross-sectional area in a plane parallel to the light-guiding surface of the light guide, the upper element having an upper height in the direction orthogonal to the light-guiding surface of the light guide, the upper element having an upper cross-sectional area in the plane parallel to the light-guiding surface of the light guide, the upper cross-sectional area being less than the lower cross-sectional area, the lower heights and the upper heights of the plurality of diffractive elements varying over the area of the light-guiding surface of the light guide.

In Example 2, the illumination system of Example 1 can optionally further comprise a light source disposed at a first edge of the light-guiding surface of the light guide and configured to direct light into the light guide, the lower heights and the upper heights of the plurality of diffractive elements varying as a function of distance away from the first edge of the light-guiding surface of the light guide.

In Example 3, the illumination system of any one of Examples 1-2 can optionally be further configured such that: the light guide is configured to guide light from the light source as guided light; the diffractive elements of the plurality of diffractive elements are configured to extract guided light out of the light guide as respective extracted light portions; and the diffractive elements of the plurality of diffractive elements have lower heights, lower cross-sectional areas, upper heights, and upper cross-sectional areas selected such that the extracted light portions have values of optical power per area that are substantially equal.

In Example 4, the illumination system of any one of Examples 1-3 can optionally be further configured such that the lower heights of the plurality of diffractive elements vary monotonically as a function of distance away from the first edge of the light-guiding surface of the light guide.

In Example 5, the illumination system of any one of Examples 1-4 can optionally be further configured such that the upper heights of the plurality of diffractive elements vary monotonically as a function of distance away from the first edge of the light-guiding surface of the light guide.

In Example 6, the illumination system of any one of Examples 1-5 can optionally be further configured such that the lower element and the upper element are substantially orthogonal to the light-guiding surface of the light guide.

In Example 7, a method for generating a diffractive optical element can comprise: depositing a thin film stack on a substrate, the thin film stack including a first layer and a second layer, the first layer being disposed between the substrate and the second layer, the first layer having a non-uniform thickness, the second layer having a non-uniform thickness; forming a first pattern on the second layer to define first areas; etching the second layer in the first areas to form first holes; forming a second pattern on the first layer in the first holes, the second pattern defining second areas, each second area being smaller than a corresponding first area; etching the first layer in the second areas to form second holes, the second holes extending fully through the first layer to depths that correspond to the non-uniform thickness of the first layer; and forming an imprint of the etched thin film stack such that the first holes and the second holes form a plurality of diffractive elements on the imprint.

In Example 8, the method of Example 7 can optionally be configured such that: the first layer is formed from a first material and is deposited by graded sputtering; the second layer is formed from a second material different from the first material and is deposited by graded sputtering; the second layer is etched with deep reactive ion etching with a first etching material that etches the second material but not the first material; the first layer is etched with deep reactive ion etching with a second etching material that etches the first material but not the second material; and the first pattern and the second pattern are formed with electron-beam lithography.

In Example 9, the method of any one of Examples 7-8 can optionally be configured such that the second layer is deposited directly on the first layer with no intervening layers between the first layer and the second layer.

In Example 10, the method of any one of Examples 7-9 can optionally be configured such that: the first layer is deposited directly on a substrate with no intervening layers between the substrate and the first layer; and the second etching material does not etch a material of the substrate.

In Example 11, the method of any one of Examples 7-10 can optionally be configured such that: the first material is amorphous silicon (Si); the second material is silicon dioxide (SiO2); the first etching material is trifluoromethane (CHF3); and the second etching material is sulfur hexafluoride (SF6).

In Example 12, the method of any one of Examples 7-11 can optionally be configured such that: the first material is silicon dioxide (SiO2); the second material is amorphous silicon (Si); the first etching material is sulfur hexafluoride (SF6); and the second etching material is trifluoromethane (CHF3).

In Example 13, the method of any one of Examples 7-12 can optionally be configured such that: the first layer is formed from a first material and is deposited by graded sputtering; the second layer is formed from the first material and is deposited by graded sputtering; a third layer is disposed in the thin film stack between the first layer and the second layer, the third layer being formed from a second material different from the first material; the first layer and the second layer are etched with deep reactive ion etching with a first etching material that etches the first material but not the second material; and the method further comprises etching the third layer in the first areas with deep reactive ion etching with a second etching material that etches the second material but not the first material, to deepen the first holes to depths that correspond to the non-uniform thickness of the second layer plus a thickness of the third layer.

In Example 14, the method of any one of Examples 7-13 can optionally be configured such that: a fourth layer is disposed in the thin film stack between the substrate and the first layer, the fourth layer being formed from the second material; and the method further comprises etching the fourth layer in the second areas with deep reactive ion etching with the second etching material, to deepen the second holes to depths that correspond to the non-uniform thickness of the first layer plus a thickness of the fourth layer.

In Example 15, the method of any one of Examples 7-14 can optionally be configured such that: the third layer has a uniform thickness; the fourth layer has a uniform thickness; and the third layer and the fourth layer are deposited by sputtering.

In Example 16, the method of any one of Examples 7-15 can optionally be configured such that: the fourth layer is deposited on a substrate with no intervening layers between the substrate and the fourth layer; and the second etching material does not etch a material of the substrate.

In Example 17, the method of any one of Examples 7-16 can optionally be configured such that: the first material is amorphous silicon (Si); the second material is silicon dioxide (SiO2); the first etching material is trifluoromethane (CHF3); and the second etching material is sulfur hexafluoride (SF6).

In Example 18, a method for generating a diffractive optical element can comprise: depositing, via sputtering, a first layer of silicon dioxide (SiO2) on a substrate, the first layer having a uniform thickness; depositing, via graded sputtering, a second layer of amorphous silicon (Si) on the first layer, the second layer having a non-uniform thickness; depositing, via sputtering, a third layer of silicon dioxide on the second layer, the third layer having a uniform thickness; depositing, via graded sputtering, a fourth layer of amorphous silicon on the third layer, the fourth layer having a non-uniform thickness; forming, with electron-beam lithography, a first pattern on the fourth layer to define first areas; etching, using sulfur hexafluoride (SF6), the fourth layer in the first areas to form first holes; etching, using trifluoromethane (CHF3), the third layer in the first areas to deepen the first holes to form deepened first holes, the deepened first holes having depths that correspond to the non-uniform thickness of the fourth layer plus the uniform thickness of the third layer; forming, with electron-beam lithography, a second pattern on the second layer within the deepened first holes to define second areas within respective deepened first holes; etching, using sulfur hexafluoride, the second layer in the second areas to form second holes; and etching, using trifluoromethane, the first layer in the second areas to deepen the second holes to form deepened second holes, the deepened second holes having depths that correspond to the non-uniform thickness of the second layer plus the uniform thickness of the first layer.

In Example 19, the method of Example 18 can further comprise: forming an imprint of the fourth layer, the third layer, the second layer, and the first layer such that the first deepened holes and the second deepened holes form a plurality of diffractive elements on the imprint, each diffractive element including a lower element extending from a base of the imprint and an upper element extending from the lower element, the lower elements having lower heights that correspond to the non-uniform thickness of the fourth layer plus the uniform thickness of the third layer, the lower elements having lower cross-sectional areas that correspond to the first areas, the upper elements having upper heights that correspond to the non-uniform thickness of the second layer plus the uniform thickness of the first layer, the upper elements having upper cross-sectional areas that correspond to the second areas.

In Example 20, the method of any one of Examples 18-19 can optionally be configured such that: the second layer has a thickness that varies monotonically from a first edge of the imprint to a second edge of the imprint; and the fourth layer has a thickness that varies monotonically from the first edge of the imprint to the second edge of the imprint.